TW201320116A - Electromagnetically absorbing, thermally conductive sheet and electronic instrument - Google Patents

Abstract

Provided is an electromagnetically absorbing, thermally conductive sheet having excellent heat conducting characteristics and electromagnetic absorbing characteristics. An electromagnetically absorbing, thermally conductive sheet (11) disposed near a high-frequency-signal-transmitting substrate (17) for transmitting a high-frequency signal, the substrate being disposed inside an electronic instrument (1), wherein the sheet is characterized in that first magnetic metallic particles and second magnetic metallic particles are included on a flexible resin material. The second magnetic metallic particles have a smaller average particle diameter and a lower electrical resistivity than first magnetic metallic particles.

Description

Electromagnetic wave absorptive heat conducting sheet and electronic machine

The present invention relates to an electromagnetic wave absorptive heat-conducting sheet which can efficiently emit heat-dissipating components such as a heat sink or a heat pipe or a heat sink from a vicinity of a signal transmitting portion for transmitting a high-frequency signal inside the electronic device, such as a semiconductor package. Conduct heat and absorb electromagnetic waves.

The present application is based on Japanese Patent Application No. 2011-178854, filed on Jan.

In recent years, electronic devices have been showing a trend of miniaturization and diversification of applications. However, power consumption has not changed, and heat dissipation measures in the machine have received increasing attention.

As a countermeasure against heat dissipation of the above-described electronic device, a heat dissipation plate, a heat pipe, or a heat sink made of a metal material having a high thermal conductivity such as copper or aluminum is widely used. The heat dissipating component having excellent thermal conductivity is disposed so as to be close to an electronic component such as a semiconductor package as a heat generating portion inside the electronic device, thereby achieving a heat dissipation effect or a temperature increase inside the device. Further, these heat dissipating components having excellent thermal conductivity are disposed at a low temperature from electronic components as heat generating portions. Further, a flexible thermally conductive sheet is disposed between the electronic component and the metal heat dissipating component to fill a gap generated when the electronic component is bonded to the metal heat dissipating component.

Since the heat dissipating component excellent in such thermal conductivity is metal, as a side effect thereof, electromagnetic induction is generated by receiving a harmonic component of an electric signal. It often causes unwanted electromagnetic radiation.

Further, the heat generating portion inside the electronic device is an electronic component such as a semiconductor element having a high current density. High current density refers to the electric field strength or magnetic field strength that may cause excess radiation. Therefore, if a heat-dissipating component made of metal is disposed in the vicinity of an electronic component, it is common to receive heat and a harmonic component of an electrical signal flowing through the electronic component.

Specifically, since the heat dissipating component is made of a metal material, the following phenomenon occurs: it functions as an antenna of a harmonic component or functions as a communication path of a harmonic noise component.

In this case, the heat transfer sheet has a function of suppressing the heat radiation component as an antenna, that is, a magnetic material is included in order to cut off the coupling of the magnetic field (Patent Document 1). Such a thermally conductive sheet has two functions of a heat conductive property and an electromagnetic wave suppressing property by including a magnetic material having a high magnetic permeability such as a ferrite or the like in a polymer material such as an organic lanthanum or an acrylic.

Patent Document 1: Japanese Laid-Open Patent Publication No. 2006-310812

The thermally conductive sheet having both of the above-described heat conduction characteristics and electromagnetic wave suppression characteristics has a characteristic change depending on the amount of the target powder contained in the polymer material as the base material.

For example, if the thermal conductivity is based on the Bruggeman formula, the following relationship exists. (Reference: "Measurement and Evaluation Techniques for High Thermal Conductivity and Thermal Conductivity of Thermal Materials for Electronic Machine Parts", Institute of Technical Information, 2003)

Here, the thermal conductivity of the entire λ _e- based sheet, the thermal conductivity of the λ _d- based thermal conductive material, the thermal conductivity of the λ _c -based base material, and the φ-based thermal conductive material account for the volume fraction of the sheet.

Further, an imaginary part μ _r " with respect to the complex magnetic permeability (μ _r = μ _r '-jμ _r ") is generally used as an index of electromagnetic wave suppression characteristics. Regarding the magnetic gas characteristics, the following relationship also exists according to, for example, the Lichtenecker formula. (Reference: "Research on Low Loss and High Dielectric Constant Magnets", Journal of Electronic Information and Communication Society, Vol. J86-C, No. 4, pp. 450-456, 2003) log(μ _r )= v ₁ ×log(μ _{r 1} )+ v ₂ ×log(μ _{r 2} )

Here, μ _r the entire sheet based complex relative permeability, complex relative permeability μ _r1 based magnetic material, the complex relative permeability μ _r2-based base material, υ ₁ based volume fraction of magnetic material, υ ₂ is the volume fraction of the base metal.

As described above, the heat conduction characteristics and the electromagnetic wave suppression characteristics significantly change depending on the filling amount of the magnetic material and the heat conductive material filled in each sheet.

However, when such an electromagnetic wave absorptive heat conductive sheet is manufactured, only the arbitrary magnetic powder and the resin are mixed, and the filling amount of the powder is limited.

When the spherical magnetic powder of the same size was most closely packed, the maximum filling ratio was 74 vol%. When more magnetic powder is filled, spherical magnetic powder having a smaller diameter is sequentially filled in the gap of the previously filled spherical magnetic powder.

In this way, when the material is filled in the resin, the intimacy with the resin It is a problem that the filling material has a small specific surface area and can be highly filled. Generally, a filler having a large particle diameter is easy to be highly filled because the specific surface area per unit volume is small.

However, when a metal magnetic particle having a large particle diameter is used as a filling substance, the magnetic permeability in the high frequency band is lowered by the skin effect, and good magnetic absorption characteristics cannot be achieved. If a metal material having a relatively high resistivity is used to alleviate such a skin effect, there is usually a problem that the thermal conductivity is small and the thermal conductivity is impaired.

The present invention has been made in view of such circumstances, and it is an object of the invention to provide an electromagnetic wave absorptive heat conductive sheet having two functions of heat conduction characteristics and electromagnetic wave absorption characteristics, and an electronic apparatus incorporating the electromagnetic wave absorptive heat conductive sheet.

In order to solve the above problems, the present invention provides an electromagnetic wave absorptive heat conductive sheet which is disposed in the vicinity of a signal transmitting portion for transmitting a high frequency signal inside an electronic device, and is characterized in that the flexible resin material contains the first magnetic metal particles and the second The magnetic metal particles, wherein the second magnetic metal particles have an average particle diameter and a specific resistance smaller than that of the first magnetic metal particles.

Moreover, the electronic device of the present invention includes: a signal transmitting unit that transmits a high-frequency signal; and an electromagnetic wave absorptive heat-conductive sheet disposed in the vicinity of the signal transmitting unit; and the electromagnetic wave-absorbing heat-conductive sheet contains the first magnetic metal particle in the flexible resin material And the second magnetic metal particles, wherein the second magnetic metal particles have an average particle diameter and a specific resistance smaller than that of the first magnetic metal particles.

In the present invention, the flexible resin material contains the first magnetic metal particles and the second magnetic metal particles, wherein the second magnetic metal particles have an average particle diameter and a specific resistance which are smaller than the first magnetic metal particles, and therefore, A thermal conductive sheet having two functions of heat conduction characteristics and electromagnetic wave suppression characteristics. Further, it is possible to provide an electromagnetic wave suppression fin having both high thermal conductivity and high electromagnetic wave suppression effect and having flexibility.

Hereinafter, embodiments will be described in detail with reference to the drawings. Further, the present invention is not limited to the following embodiments, and various modifications can be made without departing from the gist of the invention.

The electromagnetic wave absorptive heat conductive sheet to which the present invention is applied is disposed in the vicinity of a signal transmitting portion that transmits a high frequency signal inside the electronic device. The electromagnetic wave absorptive heat conductive sheet is configured to efficiently conduct heat to heat dissipating components such as a heat sink, a heat pipe, and a heat sink, and absorb electromagnetic waves, for example, from an electronic component such as a semiconductor package.

<Ply board with thermal conductive sheet>

The electromagnetic wave absorptive heat conductive sheet to which the present invention is applied is attached to, for example, the circuit board 1a inside the electronic apparatus 1 shown in Fig. 1A. That is, the sheet 11 having electromagnetic wave absorptivity and thermal conductivity as shown in Fig. 1A is disposed on the high-frequency signal transmitting substrate 17 for transmitting a high-frequency signal and the heat radiating heat radiated from the high-frequency signal transmitting substrate 17. Between the metal plates 12. Specifically, the sheet 11 is attached to the resin mold 13 that seals the semiconductor package constituting the high-frequency signal transmission substrate 17 with the one surface 11a, and the other surface 11b is adhered to the heat dissipation metal plate 12, respectively. Circuit board 1a.

The high-frequency signal transmitting substrate 17 is a specific example of a signal transmitting unit that transmits a high-frequency signal inside the electronic device 1. The copper foil 15 formed as a GND electrode on one surface of the dielectric substrate 16 is patterned on the other surface. A signal line 14 of copper is formed and constitutes a microstrip line.

The high-frequency signal transmitting substrate 17 is designed to suppress the strength of the far electric field when operating itself to a specific value or less to avoid the influence of excessive radiation. In the circuit board 1a having such a high-frequency signal transmitting substrate 17, the heat-dissipating metal plate 12, through the sheet 11, receives the harmonics of the electric signal flowing through the signal line 14 opposite to the high-frequency signal transmitting substrate 17. The component functions as an antenna of a harmonic component, and as a result, the strength of the far electric field is increased. In order to prevent the heat radiating metal plate 12 from functioning as an antenna and to realize good heat conduction characteristics, the sheet 11 contains magnetic metal particles, and the magnetic metal particles occupy the volume fraction of the sheet 11 at a specific value or more.

Further, for example, as shown in FIG. 1B, the sheet 11 having the electromagnetic wave absorbing heat transfer function to which the present invention is applied may not be in close contact with the heat dissipation metal plate 12. That is, as shown in FIG. 1B, the sheet 11 does not deteriorate the heat radiation efficiency of the heat generated by the high-frequency signal transmitting substrate 17, and absorbs the electromagnetic waves emitted from the high-frequency signal transmitting substrate 17.

Next, a specific configuration of the sheet 11 to which the present invention is applied will be described. The sheet 11 is composed of a first magnetic metal particle and a second magnetic metal particle in the flexible resin material, wherein the second magnetic metal particle has an average particle diameter and a specific resistance smaller than that of the first magnetic metal particle.

As is apparent from the performance evaluation described later, the sheet 11 having such a configuration can have both good heat conductivity and good electromagnetic wave suppression characteristics.

Then, the sheet 11 produced under the following conditions was used as an example of the electromagnetic wave absorptive heat conductive sheet, and the heat conduction characteristics and the electromagnetic wave suppression effect were evaluated.

First, a neodymium resin is used as the flexible resin material, and a spherical magnetic amorphous alloy having an average particle diameter of 6 μm is used as the first magnetic metal particles. Spherical iron powder having an average particle diameter of 1.5 μm was used as the second magnetic metal particles. In the present embodiment, the "average particle diameter" specifically means the value of the powder defined by the median diameter (also referred to as D50.), when the median diameter is divided into two by a certain particle diameter, the larger side is The smaller side is equal, for example, in this embodiment, it can be calculated using a laser diffraction, scattering method.

10 g of a coupling agent, 50 vol% of a spherical magnetic amorphous alloy and 24 vol% of spherical iron powder were added to 100 g of the epoxy resin, and stirred with a vacuum stirrer, and then made into a sheet having a thickness of 1.5 mm at 100 ° C for 30 minutes. In the environment, it is hardened to produce an electromagnetic wave absorbing heat conductive sheet.

Here, in the sheet of the embodiment, in order to realize the absorption of electromagnetic waves emitted from the high-frequency signal, for example, electromagnetic wave absorption of a band of 1 GHz or more is achieved, and a material having a specific resistance of 0.5 μΩm or more is used as the first magnetic metal particle. However, from the viewpoint of increasing the average particle diameter and improving the filling property, it is particularly preferable to use a material having a specific resistance of 0.8 μΩm or more. Further, in the sheet of the example, the resistivity of the second magnetic metal particles is smaller than the first magnetic metal particles, that is, less than 0.5 μΩm, and particularly preferably 0.3 μΩm or less, in order to achieve good thermal conductivity.

The high-resistivity magnetic metal amorphous particles are suitable as the first and second magnetic metal particles. Examples of the magnetic metal amorphous particles include Fe-Si-B based, Fe-Si-BC based, Co-Si-B based, Co-Zr based, Co-Nb based, and Co-Ta based, but not limited thereto. this.

Further, it is not limited to the magnetic metal amorphous system, and a crystalline or microcrystalline magnetic material may be used. Examples of the magnetic metal of the crystal system include Fe-based, Co-based, Ni-based, or Fe-Ni-based, Fe-Co-based, and Fe-Al. System, Fe-Si system, Fe-Si-Al system, Fe-Ni-Si-Al system, and the like. The magnetic metal of the microcrystalline system is a material obtained by adding a small amount of N, C, O, B, or the like to the crystal material to be finely crystallized.

In the sheet of the embodiment, at least one or more magnetic particles having a specific resistance of 0.5 μΩm or more and a substantially spherical shape such as a sphere or a polyhedron are used as the first magnetic metal particles, and the sheet is used as compared with The first magnetic metal particles have at least one of magnetic particles having a small average particle diameter and a specific resistance of less than 0.5 μΩm as the second magnetic metal particles.

In addition, when the average particle diameter of the second magnetic metal particles is in the range of 5 to 50% with respect to the particle diameter of the first magnetic metal, a plurality of types can be set. That is, a plurality of materials, compositions, and particle diameters can be used in combination as the second magnetic metal particles.

Further, in the sheet of the embodiment, in addition to the powder of the second magnetic metal particles, heat-conductive particles such as alumina, boron nitride, tantalum nitride, aluminum nitride, and tantalum carbide may be added to improve the thermal conductivity. . Preferably, the thermally conductive particles have a smaller particle diameter than the first magnetic metal particles and have a shape similar to a spherical shape.

Further, examples of the flexible resin include resins such as an epoxy resin, a phenol resin, a melamine resin, a urea resin, and an unsaturated polyester; or a silicone rubber, an amine ester rubber, an acrylic rubber, a butyl rubber, and an ethylene propylene rubber. Rubber, but not limited to this. Further, in the sheet of the examples, a surface treatment agent such as a flame retardant, a reaction modifier, a crosslinking agent, or a decane coupling agent may be added in an appropriate amount.

The relative complex permeability and thermal conductivity were measured to investigate the properties of the thus produced sheet.

First, the measurement of the complex permeability was carried out as follows. The prepared sheet was punched into a ring shape having an outer diameter of 20 mm and an inner diameter of 6 mm to prepare a sample for measurement. The relative complex permeability of the sample for measurement was measured using an Agilent 4291B RF Impedance/Material Analyzer manufactured by Agilent Technologies.

Further, the measurement of the thermal conductivity was carried out as follows. The prepared sheet was cut into a square having a size of about 1 cm, and the cut sample was sandwiched between a metallic heat sink and a metal heater case, and pressed at a force of 1 kgf. In the state of contact, the metal heating box is charged and heated. When the metal heating box and the metal heat sink reach a fixed temperature, the temperature difference between them is measured. The thermal conductivity is calculated according to the following formula.

Thermal conductivity = (electricity × sample thickness) / (temperature difference × measured area)

By the above measurement, the measurement result of the relative complex magnetic permeability as shown in Fig. 2 was obtained. That is, Fig. 2 shows the measurement results of the imaginary part of the relative complex permeability. Since the imaginary part of the relative complex permeability is a magnetic loss term of magnetic permeability, it can be used as an evaluation index of magnetic absorption characteristics. It can be clearly seen from Fig. 2 that the magnetic loss is large centering on 2 GHz.

The magnetic loss in the high frequency of such a magnetic metal material is mainly caused by eddy current loss and ferromagnetic resonance.

Among them, the higher the saturation magnetization of the magnetic material, the more the peak frequency of the ferromagnetic resonance shifts toward the high frequency side. The reason is that (μ _i -1) fr is proportional to Is when the initial magnetic permeability is μ _i , the resonance frequency is fr, and the saturation magnetization is Is. In the sheet-like molded article in which the magnetic particles are highly filled, the influence of the demagnetizing field is sharply reduced by the magnetic coupling between the magnetic particles, the magnetic permeability is increased, and the resonance frequency is shifted to the low frequency side, but when the saturation magnetization of the magnet is 100 A. When m ² /kg or more, the resonance frequency can be made to be in the GHz band. Therefore, in a frequency band lower than the resonance frequency, the eddy current loss becomes the main body of the magnetic loss. As a reference, Kyumura, Kubo, Kato: "Electromagnetic noise suppression heat transfer sheet", the 33rd Japan Society of Magnetic Gas Academic Lecture Summary, 14pF-14, (2009).

Further, in the spherical magnetic metal particles, the magnetic permeability due to the eddy current loss is deteriorated, and a complex eddy current factor based on Mie scattering can be used (R. Ramprasad and et al: J. Appl. Phus, 96519 (2004)) as an evaluation index.

3 is a graph showing the average particle diameter of the spherical magnetic metal particles of 6 μm, the initial magnetic permeability μ _{i of} 40, and the frequency characteristic of the imaginary part μ _r " of the relative complex magnetic permeability when the resistivity is changed, The deterioration of the magnetic permeability caused by the eddy current loss in the spherical magnetic metal particles was evaluated.

Here, the imaginary part of the relative complex permeability is normalized by using the initial magnetic permeability μ _r ". As shown in Fig. 3, if the resistivity is low, the magnetic loss is largely shifted to the low frequency layer. In the sheet using spherical magnetic metal particles having an average particle diameter of 6 μm, the resistivity must be 0.5 μΩm or more in order to make the peak of the magnetic loss in the GHz band.

Further, in order to obtain the same frequency characteristics as the sheet of the magnetic metal particles having an electric resistivity of 0.5 μΩm, an average particle diameter of 6 μm, and an initial magnetic permeability μ _i of 40, the resistivity was 1.1 μΩm, 0.9 μΩm, and 0.1. In the sheet of magnetic metal particles of μΩm, it is necessary to have an average particle diameter of 9 μm, 8 μm, or 2.8 μm, respectively. In this way, if the material has a high resistivity, even if the particle size is increased, the frequency characteristics of the high-frequency electromagnetic wave can be well absorbed. If the material has a low resistivity, the particle size must be reduced. A good frequency characteristic of absorbing high frequency electromagnetic waves is obtained.

In order to realize the frequency characteristics of the electromagnetic wave in the high frequency band as described above, the magnetic metal particles having different average particle diameters are highly filled in the flexible resin material in consideration of the following points.

First, as a method which is often used for the production of magnetic metal particles, there is an atomization method, and the particle diameter which can be produced is usually several μm to several tens of μm, and the minimum particle diameter of a material for commercial use is about 5 to 6 μm.

Therefore, as the magnetic metal particles for absorbing the electromagnetic wave absorptive sheet of the electromagnetic wave in the GHz band, for example, when a particle having an average particle diameter of 5 to 6 μm is used, it is necessary to use a material having a specific resistance of 0.5 μΩm or more.

The material for absorbing the electromagnetic wave in the GHz band is used as the first magnetic metal material, and the magnetic metal particles having a small average particle diameter are disposed as the second magnetic metal material, and are placed between the first magnetic metal materials. This increases the filling rate of the particles as a whole.

In particular, the second magnetic metal particles having a particle diameter of 5 to 50% with respect to the average particle diameter of the first magnetic metal particles are used, and the mixing ratio of the second magnetic metal particles to the first magnetic metal particles is 10 to 10 60 vol%, whereby the magnetic metal particles can be filled in the filling of the flexible resin.

Here, since the second magnetic metal particles are less susceptible to eddy current loss due to the small particle size, particles having a small specific resistance are selected from the viewpoint of improving the thermal conductivity without increasing the electrical resistivity. The reason is that since the movement of free electrons in the metal affects the thermal conductivity, the electrical conductivity is high, that is, the electrical resistance A metal material with a lower rate can increase the thermal conductivity.

In order to simultaneously have electromagnetic wave absorptivity and thermal conductivity in a favorable high frequency band, in the above embodiment, a spherical magnetic amorphous alloy having a specific resistance of 1.1 μΩm and an average particle diameter of 6 μm is selected as the first magnetic metal particles. Spherical iron powder having a specific resistance of 0.15 μΩm and an average particle diameter of 1.5 μm was used as the second magnetic metal particles. Therefore, in the sheet of the embodiment, a large magnetic loss can be obtained in the GHz band as shown in FIG. 3, and a good electromagnetic noise suppression effect can be achieved.

Moreover, in the sheet of the example, the thermal conductivity is also high, which is 2.0 W/m. K, has excellent thermal conductivity.

Here, as a comparison object, the amorphous powder having the same composition as that of the examples was used for the magnetic metal particles, and 50 vol% and 24 vol% of particles having an average particle diameter of 10 μm and 3 μm were respectively blended in the same manner as in the respective examples. The sheet was taken out and the thermal conductivity was evaluated. The thermal conductivity of the sheet of the comparison object was 1.71 W/m. K. Compared with the sheet of the comparative object, the sheet 11 of the embodiment is used as the second magnetic metal particles by using iron powder having a lower specific resistance than the amorphous powder, whereby the thermal conductivity can be increased by 18%. about.

As described above, in the sheet of the embodiment, since the skin effect is suppressed from the viewpoint of achieving electromagnetic wave absorptivity in the high frequency band, even if the first magnetic metal particle is made of a material having a high specific resistance, Since the second magnetic metal particles use a material having a low specific resistance, the thermal conductivity of the finished sheet is greatly improved.

As described above, the electromagnetic wave absorptive heat conductive sheet to which the present invention is applied is based on the flexible resin material containing the first magnetic metal particles and the second magnetic metal. In the particles, the average particle diameter and the specific resistance of the second magnetic metal particles are smaller than those of the first magnetic metal particles, so that a heat conductive sheet having both functions of heat conduction characteristics and electromagnetic wave suppression characteristics can be provided. Further, it is possible to provide an electromagnetic wave suppression fin having both high thermal conductivity and high electromagnetic wave suppression effect and having flexibility.

In particular, the electromagnetic wave absorptive heat conductive sheet can efficiently absorb the self-transmitting GHz band by selecting a material having a first magnetic metal particle having a specific resistance of 0.5 μΩm or more and selecting a material having a second magnetic metal particle having a specific resistance of less than 0.5 μΩm. The electromagnetic wave emitted by the signal transmitting unit of the domain obtains good thermal conductivity.

1‧‧‧Electronic machines

1a‧‧‧Circuit board

11‧‧‧Sheet

12‧‧‧heated metal sheet

13‧‧‧Resin mould

14‧‧‧ signal line

15‧‧‧ copper foil

16‧‧‧Dielectric substrate

17‧‧‧High frequency signal transmission substrate

Fig. 1A is a view showing the configuration of an electronic apparatus incorporating an electromagnetic wave absorptive heat conductive sheet to which the present invention is applied.

Fig. 1B is a view showing a modification of an electronic apparatus incorporating the electromagnetic wave absorptive heat conductive sheet to which the present invention is applied.

Fig. 2 is a view for explaining electromagnetic wave absorption characteristics of an electromagnetic wave absorptive heat conductive sheet to which the present invention is applied.

Fig. 3 is a view for explaining frequency characteristics relating to electromagnetic wave absorption characteristics of the electromagnetic wave absorptive thermal conductive sheet of the present invention.

1‧‧‧Electronic machines

1a‧‧‧Circuit board

11‧‧‧Sheet

11a, 11b‧‧‧ surface

12‧‧‧heated metal sheet

13‧‧‧Resin mould

14‧‧‧ signal line

15‧‧‧ copper foil

16‧‧‧Dielectric substrate

17‧‧‧High frequency signal transmission substrate

Claims (5)

An electromagnetic wave absorptive heat conductive sheet is disposed in the vicinity of a signal transmitting portion for transmitting a high frequency signal inside the electronic device, and is characterized in that the flexible resin material contains the first magnetic metal particles and the second magnetic metal particles, wherein the second The average particle diameter and the specific resistance of the magnetic metal particles are both smaller than the first magnetic metal particles. The electromagnetic wave absorptive heat conductive sheet according to claim 1, wherein the signal transmitting unit transmits a high frequency signal higher than 1 GHz, and the first magnetic metal particles have a specific resistance of 0.5 μΩm or more, and the second magnetic metal particles The resistivity is less than 0.5 μΩm. The electromagnetic wave absorptive heat conductive sheet according to claim 1, wherein the first magnetic metal particles are spherical particles. The electromagnetic wave absorptive heat conductive sheet according to claim 3, wherein a mixing ratio of the second magnetic metal particles to the first magnetic metal particles is 10 to 60 vol%, and the second magnetic metal particles are opposed to the second magnetic metal particles. The particle diameter ratio of the first magnetic metal particles is 5 to 50%. An electronic device comprising: a signal transmitting unit that transmits a high-frequency signal; and an electromagnetic wave absorptive heat-conductive sheet disposed in the vicinity of the signal transmitting unit, wherein the electromagnetic wave-absorbing thermally conductive sheet contains the first magnetic metal particles in the flexible resin material and In the second magnetic metal particles, the average particle diameter and the specific resistance of the second magnetic metal particles are both smaller than the first magnetic metal particles.